Australian energy major Origin Energy announced on August 14, 2026 that its Mortlake battery energy storage system (BESS) in south-west Victoria has completed primary commissioning and entered commercial operation. The 300 MW / 650 MWh asset sits on the site of Origin’s retired Mortlake gas-fired power station, roughly 200 kilometres west of Melbourne, and was delivered at a total investment of about A$400 million (US$279 million) with Fluence as principal contractor. The system deploys grid-forming inverter technology, which allows it to behave like a synchronous generator and actively stabilise the grid — a fundamental departure from conventional grid-following batteries that merely track the grid’s voltage and frequency. According to Australian Energy Market Operator (AEMO) data, grid-forming inverters now appear in 74% of projects across the country’s 33.2 GW battery pipeline, making Mortlake a flagship for what is fast becoming the default energy storage inverter compatibility standard for utility-scale storage.
Overview of the Technology / News
Mortlake is a repurposing story as much as a storage story. Origin is reusing the land, substation, and interconnection assets of its former open-cycle gas turbine plant rather than building from a greenfield site. This "brownfield" strategy cuts both construction cost and timeline, because the hardest and slowest part of any storage project — securing and reinforcing a high-voltage grid connection — is already largely in place. The battery essentially inherits the grid access that the gas plant once used to inject synchronous power into the Victoria grid.
The 300 MW / 650 MWh specification gives roughly 2.2 hours of storage at full rated power, a duration tuned for the National Electricity Market’s (NEM) sharp evening peak rather than for multi-hour energy shifting. That power-to-energy ratio reflects a deliberate market strategy: Mortlake is engineered to deliver fast, high-power grid services — frequency response, inertia, and voltage support — in addition to energy arbitrage, which is exactly the capability profile that grid-forming inverters unlock.
Why This Development Matters
Australia is retiring coal faster than almost any comparable grid, and each closure removes not just energy but the physical inertia and fault current that synchronous machines provide for free. Grid-forming inverters are the technological bridge: they synthesise that stability behaviour in software and power electronics, letting a battery replace a thermal plant’s system-strength role rather than just its energy. Mortlake matters because it is one of the first large Australian batteries to put that capability into commercial, revenue-earning operation at a retired thermal site.
The AEMO statistic — grid-forming inverters in 74% of a 33.2 GW pipeline — is the stronger signal. It tells you the industry has already voted: grid-forming is no longer a niche research topic but the procurement baseline for new utility storage. For anyone specifying storage today, understanding the difference between grid-forming and grid-following behaviour is no longer optional, because it determines whether a battery can participate in the system-security markets that are becoming the most valuable revenue streams.
Technical Deep Dive
The core distinction is between grid-following and grid-forming control. A grid-following inverter locks onto the grid’s voltage and frequency using a phase-locked loop and injects current to match. It is a follower — it assumes a stable grid already exists. A grid-forming inverter, by contrast, establishes and maintains its own voltage and frequency reference, acting as a controllable voltage source. In a grid disturbance, the grid-forming unit can inject or absorb power in milliseconds and provide synthetic inertia, emulating the spinning mass of a turbine. This is why grid-forming batteries can support weak grids, islanded microgrids, and high-renewable systems that grid-following assets cannot stabilise on their own.
The engineering challenge is substantial. Emulating a synchronous machine requires precise control of the power conversion system’s output impedance, fast current limiting under faults, and careful coordination between parallel inverters so they share load without fighting each other. It is a strict superset of the protection and interoperability questions captured by grid-tied inverter anti-islanding protection and hybrid inverter island mode explained at the distributed scale. The same fault-ride-through and island-detection logic that governs a residential hybrid inverter scales up into the grid-forming firmware of a utility plant — the difference is that at 300 MW, the inverter is no longer a guest on the grid but a co-host responsible for keeping it stable.
Fluence’s role is instructive. As principal contractor and inverter supplier, it has been deploying grid-forming capability through its Gridstack and Ultrastack platforms, and Mortlake represents one of the clearest public demonstrations of that technology at commercial scale in Australia. The energy storage inverter compatibility dimension — matching the inverter’s grid-support behaviour to the specific requirements of the NEM’s connection standards — is precisely where grid-forming projects succeed or fail, because the grid code compliance regime is still catching up to what the hardware can now do.
Real-world Applications
Mortlake’s primary applications are system-strength and fast-frequency services in the Victoria region, where the closure of large thermal units has thinned the synchronous generator fleet. The battery can provide inertia-like response, hold voltage during disturbances, and ride through faults — services the grid historically obtained from gas and coal turbines. By delivering these from the same asset that also arbitrages energy, Origin extracts more value per megawatt than a grid-following battery could.
The brownfield-repurposing model has immediate transferable value. Across Australia, the UK, and the US, thousands of retiring thermal plants hold prime grid-interconnection real estate that can be converted to storage at a fraction of greenfield cost and time. For the wider industry — and for the distributed segment where AGAIC operates — the same logic applies at household scale: a well-chosen energy storage inverter compatibility that can island and re-synchronise cleanly is what turns a simple battery into a genuine backup and grid-support asset.
Industry Impact / Market Implications
Mortlake cements grid-forming as a commercial, bankable capability rather than a pilot. Fluence, along with competitors like Tesla, Sungrow, and SMA, are now selling grid-forming as a standard feature, and AEMO’s grid-code work is formalising how such assets are compensated for the system strength they provide. That regulatory tailwind is what will turn grid-forming from a premium differentiator into a commodity requirement within a few years.
The cost signal matters too. Reusing the Mortlake gas plant’s connection infrastructure is expected to materially reduce the project’s delivered cost per megawatt-hour, which reinforces a broader trend: storage developers are hunting brownfield sites to dodge the grid-connection queues that now dominate project timelines. For the residential and C&I markets, this same cost curve — cheaper inverters with more capability — is what keeps improving the economics of household storage and the energy storage inverter compatibility decisions buyers face.
Future Outlook
The immediate next chapter is operational data. Mortlake will now demonstrate, in real market conditions, how a grid-forming battery monetises inertia and system-strength services, and that performance will inform AEMO’s evolving framework for procuring those services from inverter-based resources. Watch for the first published revenue figures to validate — or challenge — the premium grid-forming projects have been underwriting.
Over the next two to five years, expect grid-forming to become table stakes for new storage in high-renewable markets, and expect the brownfield-repurposing playbook to scale as the thermal fleet retires. The strategic lesson for anyone in the energy transition — from a utility planning its portfolio to a homeowner evaluating hybrid inverter island mode explained — is that the inverter is no longer a passive interface. It is the active brain of the system, and its grid-forming capability will increasingly define what a battery is worth.
